Thawing Dry Ice Drives Groovy Action on Mars

NASA's Mars Reconnaissance Orbiter has snapped a new series of false-color pictures of sand dunes that shows dramatic seasonal changes that take place in Mars' polar regions.

When the frozen carbon dioxide — called dry ice — coating the sand dunes begins to thaw and cracks, it releases jets of CO2 gas that carry dark material upward and outward, staining the surface of the frozen dunes.

The process begins at in early spring (at left in the photo above), when the ground is covered by a seasonal layer of carbon dioxide ice (dry ice) about 2 feet thick. As spring progresses the ice cracks (second panel above), releasing dark sand from the dune below. When pressurized gas trapped below the ice layer is released, it carries along sand and dust to the top of the ice layer, where it is dropped in fan-shaped deposits downhill and downwind. The final panel shows more and more of the dark dunes as the overlying layer of seasonal ice evaporates back into the atmosphere. Read more about the process here.

If a prevailing wind happens to be blowing when the gases are escaping the cracks in the ice, whatever material they are carrying will be spread by the wind across the dunes in long streaks and fans.

“It’s an amazingly dynamic process," said Candice Hansen, Planetary Science Institute, Tucson. "We had this old paradigm that all the action on Mars was billions of years ago. Thanks to the ability to monitor changes with the Mars Reconnaissance Orbiter, one of the new paradigms is that Mars has many active processes today.”

The images were taken by the High Resolution Imaging Science Experiment (HiRISE) camera aboard the Mars Reconnaissance Orbiter, which has been orbiting and observing Mars for more than six years.